NTSB Urgent Recommendation to FAA : Inspect GEnx Fan Mid Shafts Immediately .
See aviation week :
http://www.aviationweek.com/Blogs.as...c-6bb1d09569bc
And :
http://www.ntsb.gov/doclib/recletter...12-052-053.pdf
Highlights :
- The first failure (GEnx-1B) at Charleston was caused by a fractured forward end of the Fan Mid shaft (FMS), that separated at the rear of the threads.
- The fracture was no fatigue cracking.
- Further examination revealed a faceted, quasi-cleavage fracture morphology that is typical of environmentally assisted cracking of certain high strength steel alloys such as that used on the GEnx FMS.
- A second (zero flight hour) GEnx-1B FMS with a fracture was found during engine checks.
- The investigation into the cause of the environmentally assisted cracking that occurred at both fractured FMSs is continuing.
- The damage noted on the photographs of the GEnx-2B (Shanghai) is consistent with that observed on the engine that failed at Charleston.
- The GEnx-1B FMS is slightly longer than that in the -2B engine. However, the threaded end of the FMS; the manner in which it is clamped with the retaining nut and the assembly procedures, material specifications, and operating environment are similar between the two models. Therefore, the FMS in GEnx-2B engines may be susceptible to the same type of failure observed with the GEnX-1B FMS.
- the NTSB recommends that the FAA require operators to accomplish repetitive inspections of the FMS in all (on-wing and spare) GE GEnx-1B and -2B engines at a sufficiently short interval that would permit multiple inspections and the detection of a crack before it could reach critical length and the FMS.